This invention relates to ink jet compositions useful in jet printing applications, particularly "drop on demand" jet printing applications. More specifically, this invention is directed to ink jet ink compositions especially suitable for printing onto fabrics. The ink jet compositions provide low smear when applied to a substrate.
Typically, ink jet printing involves forming characters on a substrate by ejecting ink droplets from a printhead having one or more nozzles. In drop on demand ink printing systems ink droplets are expelled from a printing head when required during the printing process. The inks used must be sufficiently liquid so as to be easily ejected from the printing head. Unfortunately, due to the liquid consistency of the ink required for expulsion from the nozzle, agglomerates of the ink or puddles may form around the printhead orifices. These puddles may be of sufficient size so as to contact, and thus smear, the substrate and may even protrude into the printhead orifice hindering efficient ejection of ink and deflecting the ink from its desired trajectory to the substrate.
In addition, such puddling may provide problems during the purge step of the initial start up of the ink jet printer. Typically, ink is purged automatically from the printhead and runs down an ink jet faceplate. Generally, a narrow gap of less than 0.1 inches separates the faceplate from the substrates. Unfortunately, during the purging process conventional inks move down the faceplate in large droplets which eventually contact the substrate and deposit copious amounts of extraneous ink onto the substrate.
In view of such problems, it is desirable to provide an ink composite having a relatively high viscosity, i.e., at least 9 cps while at the same time, maintaining a relatively low surface tension.
The Kruse Patent No. 5,104,448 discloses ink jet compositions consisting of ethylene or propylene glycol ethers having low viscosity, i.e. about 5-6 cps which also have a high surface tension, i.e., greater than 25 dyne/cm.
In addition, Japanese application 59-64678 discloses ink jet compositions consisting of ethylene glycol ethers and surfactants having a surface tension below 25 dyne/cm and a preferred viscosity of less than 8 cps.